In the on site erection of metal buildings such, for example, as those having corrugated metal siding, the siding is attached to structural frames. The sliding doors for such buildings have heretofore employed wood or metal frames to which the siding panels are fastened.
In accordance with the prevailing practice the frames are constructed of prefabricated parts which are assembled at the erection site. The prior art frames, whether wood or metal, have several disadvantages. The wood frames are heavy and subject to warpage, do not remain square, and the fasteners used to attach the frame pieces together generally protrude from the door. These frames also require considerable time and expertise to assemble resulting in very expensive doors.
There are two types of metal frames in general usage, one being fabricated of extruded aluminum pieces and the other being fabricated of heavy gauge steel. Both of these types of frames are expensive. The steel frames are very heavy and thus difficult to operate while the lighter aluminum frames have poor strength characteristics.